1. Field of the Invention
The invention provides a new bacterial xylanase, a method for its production as well as a bacteria strain suitable for producing it. The invention also provides a plasmid containing a gene encoding the bacterial xylanase. The invention also provides a baking agent and a method for producing bread and baked goods using the new xylanase, wherein the xylanase increases the volume and improves the consistency of the dough.
2. Background of the Invention
In the production of yeast raised bread and baked goods, particularly in the production of white bread and rolls, it is desirable to obtain a high baking volume in the baked product. The baking volume depends on a number of factors, most of which are dependent on the properties of the flour used to form the dough. However, even when the best types of flour are used, it is still desirable to increase the baking volume. Accordingly, baking additives which increase the baking volume of bread and baked goods are desirable. Besides increasing the baking volume of baked goods made with high quality flour, it is also desirable to increase the baking volume of baked goods made with inferior types of flour.
Previous baking additives which have been found to increase the baking volume of baked goods include emulsifiers, oxidizers, reduction agents, yeast activators, enzymes such as amylases, proteases and pentosanases, pH stabilizers, mucins and fats.
For example, Kosmina ("Biochemie der Brotherstellung" [Biochemistry of Bread Production], Leipzig 1975, p. 324) disclose that although the presence of so-called "residual fractions", also referred to as mucins or tailings, in wheat flour increases the water absorption capacity of dough made from it, they also reduce the baking volume and worsen the porosity of the bread. These disadvantages can be eliminated by pretreating the "residual fractions" with a cellulase preparation made from Trichoderma viride ("MEICELASE", commercially available from Meiji).
The baking volume of dough can also be increased by adding enzymes, particularly amylases and/or proteases, to the dough, particularly when the flour used to form the dough has too low an enzyme content of its own. Unfortunately, this increases the baking volume of the dough only slightly. The incorporation of baking emulsifiers, in addition to these enzymes, results in a slight volume increase. Other additives, such as yeast activators, oxidizers and reduction agents, further increase the volume.
G. Reed ("Enzymes in Food Processing," Academic Press: New York & London, 1966, p. 253) disclose that the presence of insoluble pentosanes in flour reduces the baking volume of baked goods. To improve the baking volume, pentosanases, which reduce pentosan, were added to the bread dough. Unfortunately, the effects observed were only slight, and could not be reproduced consistently.
Rotsch ("Brot und Geback" [Bread and Pastry], 1966, p. 91) found that the effect of adding pentosanases to the bread dough could not be augmented by simultaneously adding baking emulsifiers. Thus, the effect is not additive when emulsifiers and pentosanases are used simultaneously.
Pentosanases have also been suggested as preservatives for baked goods. Cooke and Johnson (DT-AS 1,767,119) demonstrated that pentosanases were better preservatives than baking emulsifiers.
Pentosanases have also been added to rye flours which have a high pentosane-starch ratio. When this ratio is too high, the dough made with such flours has too high a viscosity, due to subsequent swelling of the rye pentosanes, and results in a baked product where the center is torn away from the crust. By adding pentosanases, the pentosanes can be reduced and the dough viscosity can be lowered accordingly. Consequently, the center does not tear away from the crust when the dough is baked.
When pentosanases are added to processed flours which have a balanced pentosane-starch ratio, the viscosity of the dough is reduced to such a degree that flat bread is formed. The addition of pentosanases is therefore advantageous only in exceptional cases, whereas it is disadvantageous in the majority of cases.
DE-A 40 17 150 describes the production of xylanase, a pentosanases, in cultures of fungus and bacteria containing beta-methyl xyloside. The properties of the xylanases formed are greatly dependent on the microorganism from which they are produced.
Baking additives according to this description are supplied under the brand name "OLYMPIAL" by Boehringer Ingelheim Backmittel GmbH, Bingen, Germany, under the brand name "ORKAN" by Ratjen-Backmittel, Flintbek, Germany, or under the brand name "S 500" by Puratos S. A., Groot-Bijgaarden, Belgium. To date, nothing has been published about the characteristics of this enzyme mixture and how it is obtained. Along with the amylase activity, a xylanase activity can also be detected in the enzyme mixture. The scope of properties of this enzyme is consistent with those of fungal xylanases which belong to the enzyme group of pentosanases. However, the effect on the baking volume of baked goods produced by the enzyme mixture is far superior to that produced by known xylanases which all originated from fungi.
Although various other baking enzymes are availiable which degrade cellulose, their effect remains far behind that of the xylanase mentioned above.